Ichirow Kaihotsu

Validation of a Dual-Pass Microwave Land Data Assimilation System for Estimating Surface Soil Moisture in Semiarid Regions

This study examines the capability of a new microwave land data assimilation system (LDAS) for estimating soil moisture in semiarid regions, where soil moisture is very heterogeneous. This system assimilates the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) 6.9- and 18.7-GHz brightness temperatures into a land surface model (LSM), with a radiative transfer model as an observation operator. To reduce errors caused by uncertainties of system parameters, the LDAS uses a dual-pass assimilation algorithm, with a calibration pass to estimate major model parameters from satellite data and an assimilation pass to estimate the near-surface soil moisture. Validation data of soil moisture were collected in a Mongolian semiarid region. Results show that (i) the LDAS-estimated soil moistures are comparable to areal averages of in situ measurements, though the measured soil moistures were highly variable from site to site; (ii) the LSM-simulated soil moistures show less biases when the LSM uses LDAS-calibrated parameter values instead of default parameter values, indicating that the satellite-based calibration does contribute to soil moisture estimations; and (iii) compared to the LSM, the LDAS produces more robust and reliable soil moisture when forcing data become worse. The lower sensitivity of the LDAS output to precipitation is particularly encouraging for applying this system to regions where precipitation data are prone to errors.

Agrometeorological conditions of grassland vegetation in central Mongolia and their impact for leaf area growth

[1] The long-term observation of surface heat and water budget and hydrometeorological elements has been carried out over a grassland site at Arvaikheer (46.23� N, 102.82� E) in central Mongolia as the framework of the GEWEX Asian Monsoon Experiment-Asian Automatic Weather Station Network (GAME-AAN). The purpose of this study is to clarify the relationship between vegetation and climate using long-term data (1982–2000) of satellite-derived leaf area index (LAI) and climatic data observed at Arvaikheer. Furthermore, we aimed to reveal physical process by comparing soil moisture and heat and water budgets in 1999 and 2000 as a case study of good and poor vegetation growth. Significant positive correlations with 99% confidence levels were found for July precipitation (P) and the LAI in July (0.538), August (0.826), and September (0.564). Composite analysis for five highest (H5) and lowest (L5) LAI years showed the significant positive anomalies of P in July and LAI in July and August for H5. In June and July 1999, soil moisture and P values were higher than values in 2000; this pattern was reversed in August and September. The mean LAI during the 1999 growing season (1.0) was about twice that of 2000 (0.6). In 1999 the ratio of evapotranspiration (ET) to P (ET/P) and change of stored soil moisture (DW )t o P( DW/P) were 0.79 and 0.15, respectively. In 2000, ET/P and DW/P were 0.94 and 0.0, respectively. These results suggest that the P and DW before July had the most influent on grass growth in central Mongolia. INDEX TERMS: 1818 Hydrology: Evapotranspiration; 1866 Hydrology: Soil moisture; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3322 Meteorology and Atmospheric Dynamics: Land/ atmosphere interactions; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; KEYWORDS: Mongolia, grassland, leaf area index, soil moisture, rainfall, evapotranspiration

Complementary relationship with a convective boundary layer model to estimate regional evaporation

An idea to use a simple convective boundary layer (CBL) model in the complementary relationship to estimate regional evaporation was explored. The CBL model simulated the potential specific humidity deficit D in CBL when the bulk stomatal resistance rst = 0. This value of D was then used in the Penman-type equation to derive evaporation Epo that would occur with ample soil moisture under the prevailing weather condition. The same equation was also used to produce the potential evaporation Ep with the actual humidity deficit, and these Ep and Epo values allowed the evaluation of the actual evaporation E by applying the complementary relationship E = ηEpo − Ep, where η is assumed as 2.0. This was tested with the data set obtained in Hexi Corridor desert area in northwestern China with a modified version of a simple CBL model developed by Lhomme (1997). It was found that the method produced better estimates of the daytime mean E values with smaller bias than those obtained from a conventional application of the complementary relationship without the CBL model. Also, it was shown that the assumption of η = 2.0 in the complementary relationship was only approximate in most cases. To take this into account, an additional procedure was explored in which η was treated as a variable, and an iteration process with the CBL model determined the final η and E values. It was found that this process produced E values that have smaller systematic error and agree better with the measurements on average, but the unsystematic error got worse than that found with η = 2.0, probably because of use of the CBL model with rst ≠ 0 in the iteration process.

Diurnal Variation of Convective Activity and Precipitable Water around Ulaanbaator, Mongolia, and the Impact of Soil Moisture on Convective Activity during Nighttime

The diurnal variations of convective activity and precipitable water were investigated using a C-band airport radar and GPS receivers around Ulaanbaator (UB), Mongolia; this location was considered as an example of an arid region. The convective activity exhibited a pronounced diurnal cycle; it increased rapidly at 1100 local solar time (LST; 0300 UTC), reached the maximum at 1400 LST, and almost disappeared after 1900 LST. On the other hand, no diurnal variation of precipitable water could be observed, which implied that there was no considerable evapotranspiration, and the diurnal variation of the convective activity was irrelevant to the variation of water vapor. The reason why the deep convection could not develop at night is discussed using numerical modeling from the viewpoint of soil moisture. In the moist soil conditions assumed for humid simulations, an increase in the water vapor in the boundary layer due to evapotranspiration led to a potentially unstable condition that was sustained until night. Deep convection was formed at the southern foot of mountains where topographical convergence was expected. On the other hand, in the dry soil conditions assumed for the arid simulations, deep convection did not occur during nighttime even though topographical convergence was expected over the southern foot of the mountains. These features of dry soil conditions were consistent with the results from radar observations around UB. In other words, since the soil around UB is too dry in practice to sustain an unstable condition until night, the deep convection had to decay by night and could not be initiated at night.

A new vegetation index derived from the pattern decomposition method applied to Landsat-7/ETM+ images in Mongolia

The goal of this study was to estimate vegetation coverage and map the land‐cover in an experimental field (60×60 km) near Mandalgobi, Mongolia using Landsat‐7/ETM+ data for ground truthing in the Advanced Earth Observing Satellite II (ADEOS‐II) Mongolian Plateau Experiment (AMPEX). We measured soil moisture, vegetation coverage, and vegetation moisture in the field at 49 grid points around the time that the Aqua satellite passed over the area. We also surveyed the land‐cover in the field. Using ground‐based data and characteristics of spectral reflectance, we attempted to extract vegetation information from satellite data using the pattern decomposition method, which is a type of spectral mixture analysis. This method uses normalized spectral shapes as endmembers, which do not change between scenes. We defined an index using the pattern decomposition coefficients to analyse sparsely vegetated areas. The index showed a linear relationship with vegetation coverage. The vegetation coverage was estimated for the study site, and the average coverage at the site was 21.4%. Land‐cover types were classified using the index and the pattern decomposition coefficients; the kappa coefficient was 0.75. The index was useful for estimating vegetation coverage and land‐cover mapping for semiarid areas.

Correction to “Agrometeorological conditions of grassland vegetation in central Mongolia and their impact for leaf area growth” by Shin Miyazaki et al.

[1] In the paper ‘‘Agrometeorological conditions of grassland vegetation in central Mongolia and their impact for leaf area growth’’ by Shin Miyazaki, Tetsuzo Yasunari, Tadashi Miyamoto, Ichirow Kaihotsu, Gombo Davaa, Dambaravjaa Oyunbaatar, Luvsan Natsagdorj, and Taikan Oki (Journal of Geophysical Research, 109, D22106, doi:10.1029/2004JD005179, 2004), the fifth and sixth authors’ names were misspelled. The correct spelling appears above. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D01105, doi:10.1029/2004JD005658, 2005

Different scale measurements of soil moisture on the ground

This study investigated spatial variability of soil moisture in experimental fields of different size on the Mongolian plateau and in Japan. Data of near surface water contents at different depths and soil physical property parameters were obtained for each field. A complicated distribution of soil moisture was seen irrespective of the size of the field and the measurement interval. Statistical analyses showed no significant correlation between water content and either plant cover or saturated hydraulic conductivity, and that the spatial scale of soil moisture depended on the size of the experimental field and the measurement interval.

Thermal inertia approach using a heat budget model to estimate the spatial distribution of surface soil moisture over a semi-arid grassland in Central Mongolia

AbstractThermal inertia is a physical parameter that evaluates soil thermal properties with an emphasis on the stability of the temperature when the soil is affected by heating/cooling. Thermal inertia can be retrieved from a heat budget formulation as a parameter when the time series of Earth surface temperature and forcing variables, such as insolation and air temperature, are given. In this study, a two-layer, linearized heat budget model was employed for the retrieval of thermal inertia over a grassland in a semiarid region. Application of different formulations to the aerodynamic conductance with respect to atmospheric stability significantly improved the accuracy of the thermal inertia retrieval. The retrieved values of thermal inertia were well correlated with in situ surface soil moisture at multiple ground stations. The daily time series of thermal inertia–derived soil moisture qualitatively agreed well with in situ soil moisture after antecedent rainfalls, which was found after fitting the time ...

Unilateral to bilateral distribution pattern of the pine wood nematode Bursaphelenchus xylophiluswithin bodies of the insect vector Monochamus alternatusdepends on nematode load

Monochamus alternatusadults carry the pine wood nematode Bursaphelenchus xylophilus. The nematodes are present in the tracheal system of vector beetles. It is known that carrying more than 10 000 nematodes causes drastic reduction in the lifespan and flight activity of beetles. To understand the effects of heavy nematode loads, 41 newly emerged M. alternatusadults were examined for lateral distribution of nematodes within the insect body. The nematodes were distributed unevenly between right and left sides of the beetle body at small nematode loads, whereas they were distributed evenly between them at heavy nematode loads. An analysis using Hagen-Poiseuille flow in a thin tube suggested that the rate of air flow decreased exponentially as the number of nematodes increased in a trachea. Thus, even distribution of nematodes between right and left sides of the vector body was considered to be responsible in part for the effects of heavy nematode loads on beetle activity.

Estimation of Plant Water Content Using ADEOS-II/GLI Data

Algorithms to estimate soil moisture using Advanced Microwave Scanning Radiometer (AMSR) data and experiments to determine their validity have been developed. Since estimations of soil moisture using AMSR data are affected by vegetation moisture content, determination of the quantity and distribution of vegetation is necessary. A variety of information can be obtained simultaneously using optical sensors such as Global Imager (GLI). In this study, we attempted to estimate plant water content using the vegetation index obtained with GLI to determine its sensitivity to vegetation coverage as well as the relationships among vegetation coverage, biomass and plant water content based on field survey data.